It is explained in EP Patent 1422436, incorporated in the present application by reference, how to form a compensating balance spring comprising a silicon core coated with silicon dioxide and cooperating with a balance having a predetermined inertia for thermal compensation of said entire resonator.
The fabrication of such a compensating balance spring offers numerous advantages but also has drawbacks. Indeed, the step of etching several balance springs in a silicon wafer offers a significant geometric dispersion between the balance springs of the same wafer and a greater dispersion between the balance springs of two wafers etched at different times. Incidentally, the stiffness of each balance spring etched with the same etch pattern is variable, creating significant fabrication dispersions.